Study of electrical and mechanical contribution to switching in ferroelectric/ferroelastic polycrystals

Polarization switching in a polycrystalline ferroelectric/ferroelastic cera mic is simulated with a finite element model. It is assumed that a crystall ite switches if the reduction in potential energy of the polycrystal exceed s a critical energy barrier per unit volume of switching material. Each cry stallite, represented by a cubic element in a finite element mesh, is a sin gle domain that switches completely without a simulated domain wall motion. The possible dipole directions of each crystallite are assigned randomly s ubject to crystallographic constraints. The model accounts for electric fie ld induced (i.e. ferroelectric) switching and stress induced (i.e, ferroela stic) switching without piezoelectric interaction. Different weights for th e mechanical and electrical contribution to switching are selected phenomen ologically to simulate electric displacement vs electric field and strain v s electric field of a ceramic lead lanthanum zirconate titanate (PLZT). Alt hough the critical energy barriers for 90 degrees and 180 degrees switching are assumed to be the same, 90 degrees switching is favored when the elect rical contribution to switching (i.e. electrical energy) is dominant, but 1 80 degrees switching is favored when the mechanical contribution to switchi ng (i.e. elastic strain energy) is dominant. With increasing mechanical con tribution and decreasing electrical contribution, the simulated electric di splacement deviates from the Rayleigh law under a low applied electric fiel d, and the shape of a switching region (or a process zone) changes from a p rolonged ellipsoid to a sphere. (C) 2000 Published by Elsevier Science Ltd on behalf of Acta Metallurgica Inc.